Non-volatile memory, due to its low energy consumption, small volume, high density, re-programmability and other characteristics, has wide applications in technology fields such as mobile communications, data terminals, multi-media, consumer electronics, defense electronic equipment, and so on.
Non-volatile memory mainly includes floating-gate non-volatile semiconductor memory and charge trapping non-volatile semiconductor memory. A floating-gate non-volatile semiconductor memory device stores charge in a floating gate formed using polysilicon. Thus, any defects related to the polysilicon floating gate can reduce charge retention time. On the other hand, a charge trapping non-volatile semiconductor memory device uses a nitride layer in place of the polysilicon. Charge is stored in the nitride layer, which is less sensitive to defects. Furthermore, compared to floating-gate non-volatile semiconductor memory, charge trapping non-volatile semiconductor memory is more suitable for miniaturization. Moreover, charge trapping non-volatile semiconductor memory has other advantages such as separated storage medium, thinner tunnel oxide layer, better data retention, and complete compatibility with microelectronics fabrication processes. Therefore, charge trapping non-volatile semiconductor memory is now expected to gradually replace floating-gate non-volatile semiconductor memory for sub-30 nm technologies.
Generally speaking, programming and erasure of a charge trapping non-volatile semiconductor memory device are done by hot-channel electron injection and hot-channel hole injection. The programming of a charge trapping non-volatile semiconductor memory device can be done by traditional hot-channel electron injection near a drain terminal. The erasure of a charge trapping non-volatile semiconductor memory device can be done by hot-channel hole injection near the drain terminal. Currently, both source and drain terminals of charge trapping non-volatile semiconductor memory devices are structured as P-N junctions.
As the device sizes shrink further, however, the channel length of the above mentioned charge trapping non-volatile semiconductor memory devices becomes shorter. When both source and drain of a charge trapping non-volatile semiconductor memory device are structured as P-N junctions, it is difficult to reduce the programming voltage, improve hot-channel electron injection efficiency, increase programming speed, and reduce energy consumption while still generating sufficient hot-channel electron or hole injections near the drain.